On bringing in an expert

I’m serious. Buy your girlfriend a private makeup class as a gift. Tip the instructor ahead of time. Let her know that you think your girlfriend wears too much makeup, and that you’d like her to discreetly teach your girlfriend how to apply more natural looks.

If that doesn’t work, you’re fucked. I promise, telling her yourself will not elicit a positive reaction, so just shut the hell up and let her keep ruining your pillows.